1. Field of the Invention
The present invention relates to a method and system for simulating movement of a patient's jaw and teeth.
2. Description of the Prior Art
In the field of orthodontics, simulation is important for treatment and correction. If the manner in which the teeth and jaw may form and grow is known, the dental practitioner is better able to diagnose problems and identify potential problems. In addition, the limits of moving teeth through braces and other correction techniques become more apparent and treatment may be carried out with more precision and greater chance of success.
Prior simulation techniques consisted of the dental practitioner observing the patient's teeth and utilizing the practitioner's knowledge and judgment to predict how the teeth would move by estimating the effects of braces and other corrective techniques. Although usually successful in correcting at least some of the structural problems, greater success rates are possible with additional information and knowledge about the patient's likely tooth movement both with and without correction.
Efforts to model tooth movement have been developed that proved to be a great aid for practitioners. Some models involve linear tooth growth, especially for those in the lower jaw. However, studies and modeling reveal that tooth movement and growth is not usually truly linearly translational. Although such modeling is helpful, with greater precision, more accurate simulations could be achieved.
Other theories that have been developed involve identifying an imaginary center of rotation for a particular tooth. Such theories as stated in papers by Pilgrim, Moses, Erdman and Hultgren, utilized instant centers of rotation to predict tooth movement along an arc centered on the instant center of rotation. It is believed that such a model is typically a better predictor of actual tooth movement than a model using straight line movement.
A further model simulates tooth movement as being governed by a linkage. The model predicts growth that is not straight line, but the arc along which the tooth moves is not centered on a single center of rotation and therefore the tooth behaves as if it was a segment of a linkage, for example, following a path as if it were mounted on one link of a four bar linkage.
Although such models have proven to be successful in providing guidance for predicting tooth growth and movement, implementation in a practical manner has proven difficult. Current techniques do not provide for accurately tracking tooth movement with sufficient precision and their relationship to the tooth's reference points. Markers and/or landmarks are necessary to ensure that the movement of the tooth or of a specific portion of the tooth are tracked. While such markers provide for improved modeling and tracking, the insertion and placement of such markers and tracking of the markers relative to one another is intrusive and only allows tracking of the marker rather than the entire tooth. A portion of the tooth moves with the marker, but it is possible that the orientation in one or more planes may have changed or other portions of the tooth may have moved in a different manner.
A further problem with such markers and/or landmarks is the precision possible in tracking the changes in position. Heretofore, tracking of markers in teeth has generally been accomplished by taking x-rays of the markers and teeth and outlining the teeth and/or markers to establish a current position. The insertion and removal of markers is intrusive and inconvenient for the patient, requiring an additional procedure. While such methods do provide for tracking of position and changes, the accuracy of such methods is decreased due to quality and resolution available for the images and the inaccuracy from manually outlining and precisely locating the markers and/or structural landmarks. As the accuracy and precision are critical for predicting small movements and in locating instant centers of rotation, such tools may not be an acceptable simulator of the teeth and their movement. Due to the precise measurements and the small distances involved, even minor errors can have a drastic adverse affect on the position of an instant center of rotation and therefore, the entire model and movement simulation, increasing the possibility for improper diagnosis and treatment.
Techniques have also been developed in orthodontics modeling to create a digital three dimensional model by scanning a casting of a patient's teeth and gums. The digital EMODEL™ digital model system provides a precise high resolution digital map of the teeth and gums, but its use has been limited in creating prostheses. Such three dimensional digital images have been used as a starting point in treatment, but have not been used to project and simulate growth and movement.
It can be seen then that a new and improved system is needed that overcomes the problems and deficiencies associated with the prior art modeling systems and methods. A system and method is needed that precisely models position and accurately simulates movement of the patient's jaw and teeth. In addition, such a system and method should provide minimal intrusion for the patient. Such a system and method should also be practical to utilize and should achieve sufficient precision and reliability for accurate simulation by the dental practitioner to diagnose problems and prescribe proper treatment. The present invention addresses these as well as other problems associated with simulating tooth growth and movement.